In systems of this type, the distributor is eliminated and each spark plug is fired by a high voltage impulse from an ignition coil shared with a companion cylinder, or by an individual coil specifically for that cylinder.
This is referred to as direct fire ignition, or waste spark.
In a waste spark system for a six cylinder engine, three ignition coils, each with their own primary and secondary windings, are combined to form one coil pack.
Each ignition coil serves two cylinders, with each end of the secondary winding attached by a high tension lead to a spark plug. These two plugs are on companion cylinders. That is, cylinders where the pistons reach top dead center at the same time. The cylinder on compression stroke is said to be the "event cylinder" and the cylinder on the exhaust stroke is the "waste cylinder".
When the high tension voltage is induced in the secondary winding, the secondary circuit is completed by current flowing through the high tension lead to the center electrode on one spark plug; bridging the gap and creating a spark in that cylinder; traveling through the cylinder block; bridging the spark plug gap in the companion cylinder; and flowing back through that high tension lead, to its starting point.
The cylinder on the compression stroke with its charge of fuel and air, is "fired" by its spark, driving the piston down on the power stroke, while the spark at the plug of the cylinder on exhaust, simply serves to complete the circuit, and is "wasted".
When the crankshaft rotates through one revolution, the roles are reversed and the waste cylinder becomes the event cylinder. Firing of both plugs again takes place, and this cylinder now drives its piston down on the power stroke.
This same process occurs on each pair of companion cylinders as they approach the top dead center position. Triggering of the primary circuit in each coil, must therefore occur at the correct time in each crankshaft revolution.
Principles of The Distributorless Ignition System (DIS)
The Distributorless Ignition System (DIS) uses several electronic sensors instead of a distributor. It also uses one coil for every two cylinders. The typical components within a DIS system are:
The crankshaft timing sensor can consist of a single Hall effect magnetic switch activated by 3 vanes on the crankshaft damper and pulley assembly. This sensor sends a signal that feeds timing and rpm information to the DIS and Electronic Control Unit (ECU) module.
The camshaft sensor is driven by the camshaft:
The DIS ignition module receives the signal from the crankshaft sensor and the camshaft sensor. It also receives the spark signal from the ECU module. The reason it does this is to ensure that they fire in the correct sequence. The DIS module also controls the engine dwell.
The basic ignition coil pack normally has multiple ignition coils. The DIS module controls these coils by means of coil leads. The ignition coils fire two spark plugs simultaneously; one on the compression stroke and one on the exhaust stroke.
The DIS system fires twice as often as a conventional ignition system and changes direction of fire. A major difference between the DIS and conventional system (contact breaker point type)is that a conventional ignition fires on the compression stroke from the center electrode to the ground electrode. But a DIS system fires on the compression stroke from the center to the ground electrode, it also fires on the exhaust stroke from the ground to the center electrode. As this requires the spark plug to fire twice as often, it necessitated the spark plugs which have platinum tipped ground and center electrodes.
Since the polarity of the primary and the secondary windings are fixed, one plug always fires in a forward direction and the other in reverse. This is different than a conventional system firing all plugs the same direction each time. Because of the demand for additional energy; the coil design, saturation time and primary current flow are also different. This redesign of the system allows higher energy to be available from the distributorless coils, greater than 40 kilovolts at all rpm ranges.
Theoretically, the advantages for using a distributorless type ignition system include:
Source: CDX Global & Wikipedia - en.wikipedia.org
